A Study On The Breakup Of An Annular Liquid Jet

The breakup and atomization of liquid jets are of theoretical importance and have been widely used in engineering, especially, in diesel engines and gas turbines etc. In various jet models, there is a kind named annular liquid jet, which commonly used in air-assist or air-blast liquid atomization. Due to the complexity of the phenomenon, the understanding of the nature and theoretical explanation are still not satisfactory. In the present work, an investigation has been conducted on the annular liquid jet.According to the linear instability theory, the dispersion equation on an annular liquid jet model is obtained. The results of calculation show the breakup mechanism of the two disturbance models with symmetric mode (n=0) and asymmetric mode (n=1,2). In other words, the effects of dimensionless quantities, such as Reynolds Number(Re),Weber Number(We),Density Ratio(Q) and Rotation Ratio(?,Γ),on the growth rate and dominant frequency of surface wave of annular liquid jet are investigated. Weber number (We) and the Reynolds number (Re) effect on both the two interfaces, therefore, these two parameters on the two disturbances will have an impact on patterns and the effects are very notable. All the dimensionless parameters (Ui, Qi, ?) relating to inner air medium have impacts on the disturbances of para-sinuous mode. All the dimensionless parameters (Uo, Qo,Γ) relating to outer air medium have impacts on the disturbances of para- varicose mode. This conclusion applies to the symmetric mode and the asymmetric modes is the same. General, under certain conditions, the disturbance growth rate on asymmetric modes is lower than the symmetric mode's.By applying shadow-graph technique and digital holography technique, macrocharacter of the annular liquid jet is obtained. Experiment results show, as to one fuel, adjusting pulse width of the injector does not change the fuel atomization quality. For different fuels (diesel and alcohol), atomization quality of alcohol is better than diesel's. This result coincides well with the theoretical results.By applying particle measurement technique based on fraunhofer diffraction and digital holography technique, the particle distribution is studied. According to the experimental results, we can see that the size distribution follows the trend like this. In the horizontal direction, the particle at the spray nozzle centerline and edges is large, and the particle in the middle is smaller. In the vertical direction, the trend emerges. The drop near the nozzle is larger, and then becomes smaller, then the particle size gradually increases, and then from small to large once again. By comparing the size of diesel and alcohol, we find that diesel particle size greater than ethanol's. This solution demonstrates that alcohol can be atomized more easily. This result coincides well with the theoretical results.From the experiment results, it can be seen that the digital holographic technology applying in the field of spraying of the internal combustion engine is feasibility.